In the process of excavating a borehole, it is currently the practice to acquire information concerning the formation through the use of methodologies known as measurement while drilling (MWD), logging while drilling (LWD), logging while tripping (LWT), and measurement while tripping (MWT). These methodologies use sensing technologies and devices such as spectral gamma ray, neutron emission and detection, radio frequency tools, nuclear magnetic resonance, acoustic imagery, acoustic density, acoustic calipers, gamma ray emission and detection, density logs, sonic logs and a range of other instrumentation to obtain detailed information concerning the formation surrounding a borehole. These measurement technologies require sophisticated devices or procedures to obtain high quality data about a formation, the level of sophistication a direct result of the severity of the downhole operating environment. Furthermore, this measurement equipment may be designed to form a component of the drilling equipment which requires further sophistication in the integration of the measurement equipment within the drilling equipment. However, the marriage of measurement equipment with standard drilling equipment is limited in both the quality and type of data which can be obtained from a borehole.
For example, where a logging or measurement tool is used within a drillstring, the type of data and the resolution of that data is limited by the material properties of the drill pipes of the drill string. In normal practice, drill pipes are steel and, accordingly, limit the ability of logging or measurement tools to acquire a broad range of information. In particular, electromagnetic and acoustic sensing devices cannot be operated from within a metal drill pipe in view of the inability of an electromagnetic or acoustic sensing device to operate through a metal drill pipe. Secondly, the use of sensing devices operable through a metal pipe may result in severe attenuation of any data signal, thereby limiting the accuracy of obtaining a data log of the formation.
Once a borehole has been fully excavated, operators often continue to acquire formation data from the borehole over the life of its production. In order to maintain stability in the borehole, it is often necessary for the borehole to be lined with a casing, normally a metal casing cemented into place. Again, the use of metal may prevent or severely attenuate the operation of sensing equipment.
Accordingly, there has been a need for tubing for use in both the drilling and casing phases of a borehole which does not prevent or severely attenuate the use of sensing equipment within the borehole. Thus, there has been a need for tubing that enables the use of a full range MWD, LWD, LWT and MWT technologies.
The drilling/borehole environment is an extremely abrasive, high stress environment that requires very high standards of performance and quality in drilling equipment. These standards and performance characteristics for drilling equipment are set forth, in part, by the American Petroleum Institute (API Specification 7 for Rotary Drill Stem Elements) and detail numerous specifications for drill pipes and casings (API Specification 5 for casings) for use in boreholes.
Thus, there has been a need for tubing which meets API specifications for drillstring components which further provide the necessary conductivity to the operating frequencies of sensing equipment used in MWD, LWD, LWT and MWT operations. Specifically, there has been a need for composite tubing conductive to radio frequency and acoustic signals which also result in a reduction of attenuation of natural decay waves/particles (gamma rays, beta particles, etc.) passing through the tubing.
It is, however, impractical for a composite tube to replace a steel drill string. Accordingly, in that the use of MWD, LWD, LWT, and MWT instrumentation requires only a relatively small window to obtain downhole data, only a corresponding short section of composite tubing is required to provide the window. Thus, the incorporation of a relatively short section of composite tubing within a drill string requires metal/composite junctions with performance characteristics equal to those of the composite and metal sections of the drillstring which thereby enable the composite tubing to be attached to metal components of the drillstring in a conventional manner. A composite drill collar will also act as a rotary torque absorber reducing the risk of twist-offs as a result of rotary torque build-up in the drillstring.
As indicated above, the downhole drilling environment is severe in terms of abrasion, pressure and temperature. In that a composite tube does not have the abrasion resistance qualities of steel, there has been a need for a composite tube with an outer surface material that reduces abrasive wear to a drilling sub or casings caused by contact with the borehole.
Conductive fibres such as carbon provide electromagnetic shielding and are often used to enhance the shielding capabilities of insulating plastics. For example, the addition of carbon fibre to nylon increases signal attenuation. Accordingly, in that it is known that the choice of carbon fibre as a material for a reinforcing medium is detrimental to the objective of EM transparency, there has been a need for a composite tube design wherein the design facilitates the use of carbon fibre while providing acceptable EM transparency.
Accordingly, there has been a need for a composite tube design wherein the composite microstructure provides both physical strength and an acceptable EM transparency to permit the use of sensing equipment from within the tube.
Still further, there has been a need for a composite drill sub with a composite structure which enhances the stiffness of the drill sub while also improving the abrasion resistance and electromagnetic transparency of the drill sub. Accordingly, there has been a need for binder compositions which are cement based which enable the elimination or partial elimination of carbon fibre from the composite structure through enhancing the stiffness of the composite drill sub.
A search of the prior art has revealed that the above problems have not been addressed. For example, U.S. Pat. No. 5,097,870, U.S. Pat. No. 5,332,049, U.S. Pat. No. 5,398,975 and PCT Publication WO 91/14123 teach composite tube structures. U.S. Pat. No. 5,250,806, U.S. Pat. No. 5,339,036 and U.S. Pat. No. 5,128,902 teach various apparatuses and methods for collecting downhole data. Canadian Patent Application 2,044,623 discloses a method for reducing noise in drillstring signals.